1. Field of the Invention
The present disclosure relates to organic light emitting diode display devices, and more particularly to an organic light emitting diode display device which can compensates for variation of characteristics of driving transistors and make time division driving of data lines.
2. Discussion of the Related Art
The OLED display device is a self light emitting device which emits a light as an electron and a hole of an organic light emitting layer therein re-couples and is expected to be the next generation display device owing to high brightness, a low driving voltage and possibility of fabrication of an extra-thin device.
Each of a plurality of pixels of the OLED display device is provided with a light emitting device having an organic light emitting layer between an anode and a cathode, and a pixel circuit for driving the light emitting device, independently. The pixel circuit is provided with a switching transistor, a capacitor, and a driving transistor, principally. The switching transistor charges a data signal to the capacitor in response to a scan pulse, and the driving transistor controls current intensity to be supplied to the light emitting device according to a data voltage charged to the capacitor for producing a gray scale.
Related art OLED display devices have the disadvantage that a non-uniform threshold voltage of the driving transistor coming from process variation causes non-uniform brightness, and variation of the threshold voltage with a time leads to brightness reduction, resulting in a reduced lifetime. In order to solve this problem, as a method for correcting the threshold voltage of the driving transistor, a method has been suggested, in which the threshold voltage of the driving transistor is sampled by using a reference voltage, and an actual data voltage is supplied to correct mobility together with the threshold voltage of the driving transistor.
However, this method has a problem in that, as the OLED display device becomes to have high definition and large sized, a time period for sampling the threshold voltage of the driving transistor becomes inadequate, leading the driving voltage of the driving transistor to rise which drops a contrast ratio. The method also has a problem in that, as the OLED display device becomes to have high definition and large sized, if a multiplexer is applied for the time division driving of the data lines, since the data line is floated in the time period for sampling the threshold voltage of the driving transistor, causing charge sharing of a parasitic capacitor of the date line and a storage capacitor increasing the driving voltage of the driving transistor and a current to the OLED, black brightness increases, to drop the contrast ratio.